feat: +/- buttons on service pills for additive/subtractive filtering

- Replace single-click service pill filter with explicit +/− buttons
- '+' adds the service to the current filter (keeps other selections)
- '−' removes the service from the current filter
- Result pills keep toggle click behavior
- Add .pill__action styles for small inline buttons

backend/frontend/style.css

@@ -376,6 +376,31 @@ input {
   background: rgba(249, 115, 22, 0.25);
 }
 
+.pill__action {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 16px;
+  height: 16px;
+  border-radius: 4px;
+  margin-left: 4px;
+  font-size: 11px;
+  font-weight: 700;
+  line-height: 1;
+  cursor: pointer;
+  color: var(--muted);
+  background: rgba(255, 255, 255, 0.06);
+  border: 1px solid transparent;
+  transition: all 0.12s ease;
+  vertical-align: middle;
+}
+
+.pill__action:hover {
+  color: var(--text);
+  background: rgba(125, 211, 252, 0.2);
+  border-color: rgba(125, 211, 252, 0.3);
+}
+
 .event h3 {
   margin: 0 0 6px;
   font-size: 17px;